WPA supplicant

When dealing with "strong" encryption of Wi-Fi networks, you have to setup a WPA or WPA2 configuration.
To handle the requirements of these protocols during association, a userspace daemon is needed: it is called a "WPA supplicant".
The most used one on Linux is wpa_supplicant; we will see here how to install and configure it.

Note:wpa_supplicant is also able to handle WEP or unencrypted connections

Other methods

You can also choose to use a custom startup script. Here is an init script example, to adapt to your Wi-Fi driver (update WIFIDRIVERS in the source) and to place into /etc/init.d/S61wifi (do not forget to give it execution rigths with chmod a+x /etc/init.d/S61wifi):